1. Field of the Invention
The present invention relates to a power supply control device, and more particularly, a power supply control device that controls a power supply connected to a motor.
2. Description of the Related Art
An image forming device in which paper is transported by rollers and an image is formed (i.e. printed) on that paper (e.g. an MFP (Multi-Function Peripheral) that features scanning, facsimile, copying, printing, data communication and server functions, or a facsimile device, a copier, a printer or the like) includes a motor for driving a paper transport roller, a developing device, an intermediate transfer belt or the like.
Conventionally, a motor is generally controlled by consuming regenerative energy from the motor by resistance to generate heat. Alternatively, regenerative energy may be accumulated by an accumulator, in which case the accumulator may be connected to, or disconnected from, the power supply line depending on the voltage of the accumulator.
Document 1, specified below, discloses a device that utilizes regenerative energy from a DC motor in which a battery is charged with regenerative power from the motor. The battery is connected to the drive power supply for the motor via a switch and energy accumulated in the battery is used when the motor is started up.
Document 2, specified below, discloses a switching power supply device in which, when the motor drive voltage exceeds a predetermined level, a battery is charged with regenerative energy from the motor, which is then used during the energy-saving mode.    [Document 1] JP 2005-278348 A    [Document 2] JP 2006-180629 A
In an image forming device with high-speed operation, the slowing-down time of the motor must be minimized. To shorten the slowing-down time, the rotational energy that the motor has must be quickly disposed of.
On the other hand, a method that consumes regenerative energy from the motor by resistance to generate heat wastes valuable energy.
If regenerative energy is accumulated in an accumulator and is connected directly to a power supply line depending on the accumulated voltage, the voltage on this power supply line varies significantly. Therefore, this method cannot be used with a load that requires high precision in voltage. Furthermore, it is difficult to supply current from an accumulator when a large amount of current is required. Therefore, switching is necessary to supply current from an accumulator during energy saving or under other conditions.
In other words, if the technique of Document 1 is employed, the battery accumulating regenerative power from the motor is directly connected to the motor drive power supply, leading to unstable voltage, making the technique unsuitable for a drive power supply for a motor or the like.
The technique of Document 2 also provides a configuration in which the battery is charged during regeneration and is then connected directly to the output in response to an energy-saving mode signal, and is disconnected when the motor drive voltage becomes sufficiently low. Thus, the output voltage varies significantly. Another problem is that the energy saving mode signal must be provided.